Method of alloying a semiconductor device

ABSTRACT

A method for alloying a semiconductor substrate upon which wordlines enclosed in spacers have been formed, with the substrate exposed between the wordlines. A thin sealing layer is deposited over the substrate and the wordlines, the sealing layer helping to maintain the alloy in said substrate. The alloying material employed in the substrate is hydrogen and optionally monatomic hydrogen. Alloying the substrate with monatomic hydrogen may also be done after deposition of a metal layer, or at other process steps as desired.

[0001] This application is a divisional of U.S. patent application Ser.No. 10/304,194, filed on Nov. 25, 2002, which is a continuation of U.S.patent application Ser. No. 08/555,801, filed on Nov. 9, 1995, both ofwhich are incorporated herein by reference.

BACKGROUND OF THE INVENTION

[0002] 1. The Field of the Invention

[0003] The present invention relates to the manufacture of semiconductordevices. More particularly, the present invention is directed to animproved method of alloying a semiconductor device during themanufacture thereof.

[0004] 2. The Relevant Technology

[0005] Hydrogen alloying, or annealing in a hydrogen atmosphere, is usedto heal damage caused to the lattice structure of the crystallinesemiconductor substrate by the various processes used to form circuitstructures. Hydrogen, in the alloying process, forms bonds with damagedareas of the substrate, tying up dangling bonds of substrate atoms andimproving the electrical properties of the substrate.

[0006] Hydrogen alloying is typically employed near the end of anintegrated circuit fabrication procedure, after all circuit devices havebeen formed. Some typical structures present on a semiconductorsubstrate during such post-metal alloying are shown in cross section inFIG. 1.

[0007]FIG. 1 shows a partial cross section of a semiconductor device.Semiconductor substrate 12, typically a silicon substrate, has anisolation region 14, typically field oxide, which has been grownthereon. Wordlines 16 each enclosed in spacers 18 are formed oversubstrate 12 and isolation region 14. A thin etch-stop and sealing layer20, typically silicon nitride, is present on substrate 12 and isolationregion 14 except where plugs 24 contact substrate 12. Plugs 24 areformed of an electrically conductive material and extend from substrate12 up through a first dielectric planarization layer 22. A capacitorstructure including capacitor plate 26, thin dielectric layer 28, andcapacitor plate/ground line 30 is formed in contact with one plug 24. Incontact with the other plug 24 is a conductive-material via 34,typically formed of metal, which extends upward from the other plug 24through a second dielectric planarization layer 32 to aconductive-material bitline 36, also typically formed of metal.

[0008] The typical hydrogen alloying step is performed upon structuresidentical to or similar to those shown in FIG. 1. Sealing layer 20 isrelatively impervious to diffusion of various dopants, includinghydrogen. Other structures formed on substrate 12 can also impede thediffusion of hydrogen somewhat. Thus, the path hydrogen must take todiffuse into substrate 12 typically takes the form of path P shown inFIG. 1. The hydrogen must typically pass through or around bitline 36,along via 34 and plug 24 and down into substrate 12 to alloy substrate12 in region R. As circuit density in semiconductor devices increases,diffusion of hydrogen along path P of FIG. 1 becomes lengthy and moredifficult, such that adequate hydrogen alloying of substrate 12 cannotbe achieved. Thus an improved hydrogen alloying method is needed.

SUMMARY OF THE INVENTION

[0009] An object of the present invention is to provide a method ofalloying a semiconductor device, said method providing adequate alloyingeven in highly dense devices.

[0010] Still another object of the present invention is to provide arapid method of alloying a semiconductor device.

[0011] Still another object of the present invention is to provide amethod of alloying a semiconductor device in situ with existing processsteps.

[0012] In accordance with one preferred method of the present invention,alloying is performed upon a substrate on which wordlines enclosed inspacers have been formed, with the substrate exposed between thewordlines. A thin sealing layer is then deposited over the substrate andthe wordlines, the sealing layer helping to maintain the hydrogen in thesubstrate. The hydrogen employed in alloying the substrate is optionallymonatomic hydrogen.

[0013] According to another preferred method of the present invention,alloying is performed with monatomic hydrogen at a post-metal alloyingstep. Alloying with monatomic hydrogen may also be used at other processsteps as desired.

[0014] Alloying while the substrate is still directly exposed can allowfor a greater alloy concentration. The thin sealing layer depositedthereafter helps maintain the alloy concentration, such that subsequentdamage to the substrate may be repaired in situ.

[0015] Alloying with monatomic hydrogen increases the diffusivity andreactivity of the hydrogen, allowing shorter process times and lowertemperatures to achieve the same alloying effect.

[0016] These and other features of the present invention will becomemore fully apparent from the following description and appended claims,or may be learned by the practice of the invention as set forthhereinafter.

BRIEF DESCRIPTION OF THE DRAWINGS

[0017] In order that the manner in which the above-recited and otheradvantages of the invention are obtained may be more fully explained, amore particular description of the invention briefly described abovewill be rendered by reference to specific embodiments thereof which areillustrated in the appended drawings. Understanding that these drawingsdepict only typical embodiments of the invention and are not thereforeto be considered limiting of its scope, the invention will be describedand explained with additional specificity and detail through the use ofthe accompanying drawings in which:

[0018]FIG. 1 is a partial cross section of a semiconductor device,showing the path P of hydrogen diffusion during post-metal alloying.

[0019]FIG. 2 is a partial cross section of a partially formedsemiconductor device after formation of wordlines enclosed in spacers,showing the path P of hydrogen to a substrate according to one method ofthe present invention.

[0020]FIG. 3 shows the cross section of FIG. 2 after deposition of athin sealing layer.

[0021]FIG. 4 is a schematic representation of some equipment useful inone method of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

[0022] The present invention provides improved methods for alloying asemiconductor device, particularly the substrate thereof.

[0023] According to one preferred method of the present invention, thealloying is performed at an early step of the fabrication process,rather than post-metal as illustrated in FIG. 1. A post-metal alloyingstep may optionally be employed in addition to the earlier alloyingstep.

[0024] As shown in FIG. 2, at an earlier typical processing step,wordlines 16 enclosed in spacers 18 have been formed over substrate 12and isolation region 14. Substrate 12 or isolation region 14 is exposeddirectly except at the locations of wordlines 16. According to apreferred method of the present invention, the semiconductor device isalloyed at the processing step represented in FIG. 2. The alloyingmaterial will preferably be hydrogen. The alloying material may alsoinclude, in addition to hydrogen, an inert gas and/or nitrogen. By wayof example, the inert gas can be argon, helium, or a mixture of both.The alloying material, which has direct access to substrate 12, thentravels path P of FIG. 2 to reach substrate 12.

[0025] Immediately after alloying, a thin sealing layer 20, preferablysilicon nitride but possibly alumina or layered nitride and oxide, isdeposited over substrate 12 and all structures thereon, as shown in FIG.3. Thin sealing layer 20 remains through subsequent processing in thesemiconductor device over substantial areas of the substrate. This isseen in FIG. 1, where portions of thin sealing layer 20 remain. Thinsealing layer 20 is more impervious to the alloying material, helping toretain the alloying material in substrate 12. This allows the alloyingmaterial to remain in the substrate and repair substrate damage at laterfabrication steps. The earlier alloying also assists in assuringsufficient total alloying after an optional post-metal alloying step.

[0026] Thin sealing layer 20 is already present in typical processing inthe form of a thin nitride layer which serves as a diffusion barrier andan etch stop. Thus, the above preferred method of the present inventionmay be beneficially incorporated into the nitride deposition process. Astandard nitride deposition chamber such as an LPCVD reactor or furnacemay be used first to alloy the substrate in a hydrogen atmosphere attemperatures of preferably 400° C. or greater. The hydrogen is thenevacuated, a vacuum drawn, and the typical LPCVD nitride depositioncarried out. The preferred method is a plasma enhanced LPCVD. This insitu hydrogen alloying avoids adding process steps and provides maximumhydrogen content at the time the thin sealing layer of nitride isdeposited.

[0027] According to another preferred method of the present invention,the semiconductor device is alloyed in an atmosphere substantiallycomprised of monatomic hydrogen instead of the typical diatomichydrogen. Monatomic hydrogen may be provided as illustrated in FIG. 4 bypassing hydrogen from a hydrogen source 104 through an energy sourcesuch as ionizer 102 and thence to a process chamber 108. Ionizer 102 maytake many forms, including an ultraviolet light source, an RF generator,an electron beam ionizer, an ECR plasma generator, and the like.Alternatively, monatomic and ionized hydrogen may be created fromdiatomic hydrogen in the process chamber itself by an RF plasma or othertypical means. Hydrogen ions may optionally be accelerated by apotential difference such as a biased substrate or substrate holder.Hydrogen ions may optionally also be guided, focused, or filteredthrough the use of magnetic fields.

[0028] The use of monatomic hydrogen in this preferred method of thepresent invention has several benefits. Monatomic hydrogen presents asmaller cross section, diffusing more rapidly through the relativelylong path P for post-metal anneal as shown in FIG. 1. Monatomic hydrogenis also more reactive than diatomic hydrogen, allowing the diffusedhydrogen to more rapidly tie up dangling bonds in the substrate. Thisgreater diffusivity and greater reactivity allow shorter processingtimes in furnace applications.

[0029] Monatomic hydrogen alloying may be used at post-metal alloying.Monatomic hydrogen alloying may also be used in conjunction with thefirst preferred method discussed above, early in the fabrication processjust before depositing a thin layer of nitride. Monatomic hydrogenalloying may also be performed in situ before or after existing processsteps, such as before the thin nitride deposition as discussed above, orafter a dry etch in the same process chamber, or at any other processpoint at which substrate repair is needed.

[0030] The present invention may be embodied in other specific formswithout departing from its spirit or essential characteristics. Thedescribed embodiments are to be considered in all respects only asillustrative and not restrictive. The scope of the invention is,therefore, indicated by the appended claims rather than by the foregoingdescription. All changes which come within the meaning and range ofequivalency of the claims are to be embraced within their scope.

What is claimed is:
 1. A semiconductor device, comprising: asemiconductor substrate with at least one electrical device thereon, thesemiconductor substrate having at least a portion thereof alloyed with amaterial comprising hydrogen; and a sealing layer over the semiconductorsubstrate and the at least one electrical device, the sealing layeradapted to assist in retaining in the semiconductor substrate thealloyed material comprising hydrogen.
 2. The semiconductor device ofclaim 1, wherein the semiconductor substrate comprises a siliconsubstrate and the sealing layer comprises silicon nitride.
 3. Thesemiconductor device of claim 1, wherein the alloyed material comprisesmonatomic hydrogen.
 4. The semiconductor device of claim 1, wherein thealloyed material comprises monatomic hydrogen and ionized hydrogen.
 5. Asemiconductor device, comprising: a silicon substrate with at least oneelectrical device thereon, the silicon substrate having at least aportion thereof alloyed with a material comprising monatomic hydrogenand ionized hydrogen; and a sealing layer comprising silicon nitrideover the silicon substrate and the at least one electrical device, thesealing layer adapted to assist in retaining in the silicon substratethe alloyed material comprising monatomic hydrogen and ionized hydrogen.6. A semiconductor substrate of an integrated circuit device,comprising: a silicon substrate with at least one electrical devicethereon, the silicon substrate having at least a portion thereof alloyedwith a material comprising monatomic hydrogen; and a sealing layercomprising silicon nitride over the silicon substrate and the at leastone electrical device, the sealing layer adapted to assist in retainingin the silicon substrate the alloyed material comprising monatomichydrogen.
 7. The semiconductor device of claim 6, wherein the alloyedmaterial comprises monatomic hydrogen and ionized hydrogen.